I am trying to build custom Linux image and add custom packages employing make buildroot-menuconfig. I have tried to add python and other text editors (joe), and some custom files and dirs into /opt directory, as well. Menuconfig saved configuration to freedom-u-sdk/work/buildroot/.config location, but image produced doesn’t contain any packages I tried to include. However, MD5 sums for new and default images are different. I also tried to change root password, just to be sure, but when I boot linux using newly produced image, the password is the default one - sifive. I also observed awkward behavior in menuconfig - it isn’t possible to delete characters in string value fields (i.e. root password), only to add.
I suspect your problem stems from this line in the freedom-u-sfk/Makefile:
$(MAKE) -C $< RISCV=$(RISCV) PATH=$(PATH) O=$(buildroot_wrkdir) riscv64_defconfig
… That is probably overwriting your configuration changes with the default values. Try remove that line.